1. Field of the Invention
The present invention relates to a wide angle radiant energy detection apparatus, and more particularly to such apparatus wherein the optical elements are arranged to minimize vignetting caused by optical element support structure. 2. Description of the Prior Art
Radiant energy detection systems, such as are utilized in heat seeking guided missiles, or in missiles designed to home on laser illuminated bodies generally operate to first detect a target, and then follow it to a point of impact. In so doing, the optical portion of the apparatus systematically explores or scans a predetermined spatial region, and examines energy collected therefrom to determine whether or not an object of interest is present. If such an object is detected, the scanning phase terminates and the system enters a tracking mode to guide the missile towards the object.
The bore sight axis of such a system is, in effect, projected into space and becomes the axis of a conical geometric figure, the apex of which lies within the detection system itself. The energy collected from within the conical spatial region is detected and converted into a varying electrical signal which is proportional to changes in the amount of radiant energy received.
Detection of a radiant energy emitting source during the scanning phase is customarily performed by mechanically driving the optical components to execute a cyclic scanning action which results in the exploratory examination of a conical spatial region greater in size than the instantaneous field of view of the optical system itself. The components so driven usually comprise the mirrors and lenses from or through which intercept energy is directed to a detector.
Upon detection of radiant energy indicating the presence of a radiant energy emitting source within the spatial region under examination, cyclic movement of the optical elements ceases and the system switches to the track mode of operation. Generally, the track mode incorporates means for feeding the target representative electrical signals to an error detector, and then to a servo mechanism which controls the missile trajectory in accordance with target movement. As long as seeker gimbal angles and tracking rate capacities are not exceeded, any evasive action by the target is ineffective to prevent impact.
In a system of this type, the instantaneous field of view of the optical unit affects primarily the scanning phase operation of the system. A relatively narrow field of view requires more scanning action to search for a target in a given area, and is a significant limitation on the system because more time is required for target acquisition. This limitation increases the vulnerability of the missile to destruction before accomplishment of target impact.
A second significant factor affecting target acquisition is the amount of radiant energy that the optical system can gather to focus on the detector. A limitation of previous systems has been the manner in which optical elements are supported. The structural members intercept a significant portion of the radiant energy entering the optical system, thereby reducing the amount available for target acquisition. These problems have been overcome by the present invention which utilizes a lens as a structural support to reduce the vignetting losses, and improve angular resolution at wide field angles.